Charged control device and battery pack employing it

ABSTRACT

A battery pack employing a charge control device includes a charge detection circuit for checking whether a secondary cell is in a charged state or not based on at least a charge voltage or a charge current of the secondary cell; a control circuit for controlling feeding of electric power to the secondary cell according to an output of the charge detection circuit; and a setting circuit for setting a level of the charge voltage or the charge current at which the charge detection circuit recognizes the charged state according to control information.

This application is a Continuation of co-pending U.S. patent applicationSer. No. 11/092,977 filed on Mar. 30, 2005, which is aContinuation-In-Part of U.S. patent application Ser. No. 10/316,152filed on Dec. 11, 2002 that issued as a U.S. Pat. No. 6,894,458 on May17, 2005, and claims the benefit of the Japanese patent Application No.2001-376771 filed on Dec. 11, 2001 in Japan.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charge control device for controllingthe charging of a secondary cell or battery (hereinafter collectivelyreferred to as a “secondary cell” throughout the specification and theclaims) by monitoring its charge state, and relates also to a batterypack employing such a charge control device.

2. Background of the Related Art

FIG. 6 is a diagram showing circuit configuration of a related artbattery pack incorporating a charge control device. The battery pack 1′shown in this figure is composed of a rechargeable secondary cell 2′, acharge control IC 3′ for controlling the charging of the secondary cell2′ by monitoring its charge state, feed terminals 4 a′ and 4 b′ to whichdirect-current electric power is fed from a charger (not shown), aswitch device 5′ connected between the feed terminal 4 a′ and thepositive electrode of the secondary cell 2′, and a sense resistor 6′connected between the negative electrode of the secondary cell 2′ andthe feed terminal 4 b′ (ground line). The sense resistor 6′ has a verylow resistance (generally a few tens of mΩ), which permits the chargecurrent flowing through the secondary cell 2′ to be detected as avoltage.

The charge control IC 3′ is built by sealing into a single package afirst full charge detection circuit 31′ for checking whether thesecondary cell 2′ is in the fully charged state or not by comparing itscharge voltage with a predetermined reference voltage, a direct-currentvoltage source 32′ for generating the reference voltage, a second fullcharge detection circuit 34′ for checking whether the secondary cell 2′is in the fully charged state or not by comparing the voltages at bothends of the sense resistor 6′, and a control circuit 35′ for controllingthe feeding of electric power to the secondary cell 2′ by turning on andoff the switch device 5′ according to the output signals of the firstand second full charge detection circuits 31′and 34′.

As described above, the charge control IC 3′ can monitor the chargestate of the secondary cell 2′ and control its charging in aconsiderably satisfactory manner in this battery pack 1′.

However, in the charge control IC 3′ configured as described above, thereference voltage generated by the direct-current voltage source 32′(i.e., the level of the charge voltage at which the first full chargedetection circuit 31′ recognizes the fully charged state) is fixed atthe time of circuit fabrication. This makes it impossible to cancelfactors that cause variations in the reference voltage after the circuitfabrication (for example, the influence of stress occurring when thecharge control IC 3′ is packaged or mounted on a circuit board) andfabrication-associated variations in the secondary cell 2′ itself, whichis the target of monitoring by the charge control IC 3′. Thus, in thecharge control IC 3′ configured as described above, the fully chargedstate voltage level needs to be set rather low to ensure safe chargingoperation. This makes it impossible to make the most use of the chargecapacity of the secondary cell 2′.

On the other hand, the second full charge detection circuit 34′ is soconfigured to check whether the secondary cell 2′ is in the fullycharged state or not by comparing the voltages at both ends of the senseresistor 6′, which is connected external to the charge control IC 3′.Therefore, by setting the resistance of the sense resistor 6′appropriately, it is possible to vary the level of the charge current atwhich to recognize the fully charged state. However, since the senseresistor 6′ has a very low resistance, it tends to be influenced byvariations in connection, wiring resistances, and other factors.Accordingly, this makes it extremely difficult to correct a variation inthe voltage level at which the fully charged state is recognized. Thus,in the charge control IC 3′ configured as described above, the level ofthe charge current at which the fully charged state is recognized alsoneeds to be set rather low to ensure safe charging operation. And, thismakes it impossible to make the most use of the charge capacity of thesecondary cell 2′. Moreover, the sense resistor 6′, connectedexternally, hampers the scaling-down and cost reduction of the batterypack 1′.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a charge controldevice and battery pack employing it that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a charge control devicethat can accurately control the charging of a secondary cell bycanceling the influence of stress occurring when an IC is packaged ormounted on a circuit board and other factors, and to provide a batterypack employing such a charge control device.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the chargecontrol device and battery pack employing it includes a charge controldevice having a charge detection circuit for checking whether asecondary cell is in a charged state or not based on at least a chargevoltage or a charge current of the secondary cell; a control circuit forcontrolling feeding of electric power to the secondary cell according toan output of the charge detection circuit; and a setting circuit forsetting a level of the charge voltage or the charge current at which thecharge detection circuit recognizes the charged state according tocontrol information fed in directly from outside.

In another aspect, a battery pack employing a charge control deviceincludes a charge detection circuit for checking whether a secondarycell is in a charged state or not based on at least a charge voltage ora charge current of the secondary cell, a control circuit forcontrolling feeding of electric power to the secondary cell according toan output of the charge detection circuit; a control informationgeneration circuit for generating control information based on anexternal signal fed in directly from outside; and a setting circuit forsetting a level of the charge voltage or the charge current at which thecharge detection circuit recognizes the charged state according to thecontrol information outputted from the control information generationcircuit.

In another aspect, a battery pack employing a charge control deviceincludes a charge detection circuit for checking whether a secondarycell is in a charged state or not based on at least a charge voltage ora charge current of the secondary cell; a control circuit forcontrolling feeding of electric power to the secondary cell according toan output of the charge detection circuit; a control informationgeneration circuit for generating control information by converting ananalog external signal fed in directly from outside into digital data;and a setting circuit for setting a level of the charge voltage or thecharge current at which the charge detection circuit recognizes thecharged state according to the control information outputted from thecontrol information generation circuit.

In another aspect, a battery pack employing a charge control deviceincludes a charge detection circuit for checking whether a secondarycell is in a charged state or not based on at least a charge voltage ora charge current of the secondary cell; a control circuit forcontrolling feeding of electric power to the secondary cell according toan output of the charge detection circuit; a control informationgeneration circuit for generating control information based on an outputresult of the control circuit; and a setting circuit for setting a levelof the charge voltage or the charge current at which the chargedetection circuit recognizes the charged state according to the controlinformation outputted from the control information generation circuit.

In another aspect, a battery pack employing a charge control deviceincludes a charge detection circuit for checking whether a secondarycell is in a charged state or not based on at least a charge voltage ora charge current of the secondary cell; a control circuit forcontrolling feeding of electric power to the secondary cell according toan output of the charge detection circuit; a detection circuit, providedwithin the charge control device, for detecting a state of the chargecontrol device; a control information generation circuit for generatingcontrol information based on a signal outputted from the detectioncircuit; and a setting circuit for setting a level of the charge voltageor the charge current at which the charge detection circuit recognizesthe charged state according to the control information outputted fromthe control information generation circuit.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates a battery pack incorporated with a charge controldevice of a first exemplary embodiment of the present invention;

FIG. 2 illustrates a battery pack incorporated with a charge controldevice of a second exemplary embodiment of the present invention;

FIG. 3 illustrates a battery pack incorporated with a charge controldevice of a third exemplary embodiment of the present invention;

FIG. 4 illustrates a battery pack incorporated with a charge controldevice of a fourth exemplary embodiment of the present invention;

FIG. 5 illustrates a battery pack incorporated with a charge controldevice of a fifth exemplary embodiment of the present invention; and

FIG. 6 illustrates a battery pack incorporating a related art chargecontrol device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a circuit configuration of a battery pack incorporating acharge control device of a first exemplary embodiment of the presentinvention. The battery pack 1 of the first exemplary embodiment iscomposed of a rechargeable secondary cell 2 (for example, a lithium ioncell), a charge control IC 3 for controlling the charging of thesecondary cell 2 by monitoring its charge state, feed terminals 4 a and4 b to which direct-current electric power is fed from a charger (notshown), and a switch device 5 (for example, a MOS transistor) connectedbetween the feed terminal 4 a and the positive electrode of thesecondary cell 2.

The charge control IC 3 is built by sealing into a single package afirst full charge detection circuit 31 for checking whether thesecondary cell 2 is in the fully charged state or not by comparing itscharge voltage with a predetermined reference voltage, a variabledirect-current voltage source 32 for generating the reference voltage, asense resistor 33 connected between the negative electrode of thesecondary cell 2 and the feed terminal 4 b (ground line), a second fullcharge detection circuit 34 for checking whether the secondary cell 2 isin the fully charged state or not by comparing the voltages at both endsof the sense resistor 33, a control circuit 35 for controlling thefeeding of electric power to the secondary cell 2 by turning on and offthe switch device 5 according to the output signals of the first andsecond full charge detection circuits 31 and 34, an offset circuit 36for offsetting the level at which the second full charge detectioncircuit 34 inverts its output, and the feed terminal 4 c feeding thecontrol information steadily from outside the charge control device tothe variable direct-current voltage source 32 and the offset circuit 36.

The output signal level of the first full charge detection circuit 31 islow (at the logical low level) or high (at the logical high level)according to whether the charge voltage of the secondary cell 2 is loweror higher, respectively, than the reference voltage generated by thevariable direct-current voltage source 32. On the other hand, the outputsignal level of the second full charge detection circuit 34 is low orhigh according to whether the voltage across the sense resistor 33 ishigher or lower, respectively, than the offset level set by the offsetcircuit 36.

When one of the output signal levels of the first and second full chargedetection circuits 31 and 34 becomes high, the control circuit 35recognizes that at least one of the charge voltage and charge current ofthe secondary cell 2 indicates the fully charged state, and opens theswitch device 5. With this configuration, it is possible to prevent thesecondary cell 2 from being overcharged.

Here, the variable direct-current voltage source 32 of the firstexemplary embodiment can set the aforementioned reference voltage (i.e.,the level of the charge voltage at which the first full charge detectioncircuit 31 recognizes the fully charged state) according to the controlinformation read from outside the charge control device through the feedterminal 4 c. Moreover, the offset circuit 36 of this embodiment can setthe aforementioned offset level (i.e., the level of the charge currentat which the second full charge detection circuit 34 recognizes thefully charged state) likewise according to the control information readfrom outside the charge control device through the feed terminal 4 c.

With the above described configuration, the charge control IC 3 of thefirst exemplary embodiment of the present invention can easily changethe set levels of the charge voltage and charge current at which thefully charged state is recognized, even after the charge control IC 3 ispackaged or mounted on a circuit board, or after the secondary cell 2 isconnected.

Accordingly, even after the charge control IC 3 is built into thebattery pack 1, it is possible to optimize the levels of the chargevoltage and charge current at which to recognize the fully charged stateby canceling all factors that cause variations in the reference voltageafter the fabrication of the circuit (for example, the influence ofstress occurring when the charge control IC 3 is packaged or mounted ona circuit board) and all fabrication-associated variations in thesecondary cell 2 itself, which is the very target of monitoring by thecharge control IC 3.

In the related art charge control IC 3′ (FIG. 6), the fully chargedstate levels are set rather low to ensure safe charting operation,because approximately ±0.5% variations are inevitable in the chargevoltage detected level and charge current detected level. However, inthe preferred embodiments of the present invention, when detected levelsare reduced to ±0.1% or smaller, it is not necessary to lower the levelsof the fully charged state of both circuits 31 and 34. This makespossible to use of the charge capacity of the secondary cell 2 moreeffectively.

FIG. 2 is a circuit configuration of a battery pack incorporating acharge control. device of a second exemplary embodiment of the presentinvention. The numbers appearing in FIG. 2, which are identical to thoseof FIG. 1, correspond to the same circuit elements as described inreference to the first exemplary embodiment of the present invention.Accordingly, written descriptions for identical circuit elements in FIG.2 are omitted.

As shown in FIG. 2, a control information generation circuit 37 receivesan external signal from outside through the feed terminal 4 c, and thecontrol information generation circuit 37 feeds the control informationto the variable direct-current voltage source 32 and the offset circuit36. In the second exemplary embodiment of the present invention, theexternal signal fed from outside to the control information generationcircuit 37 includes a history signal (i.e., a history signal indicatingthe number of times that the cell has been charged thus far). Thecontrol information generation circuit may include a microcomputer.

FIG. 3 is a circuit configuration of a battery pack incorporating acharge control device of a third exemplary embodiment of the presentinvention. The numbers appearing in FIG. 3, which are identical to thoseof FIG. 1, correspond to the same circuit elements as described inreference to the first exemplary embodiment of the present invention.Accordingly, written descriptions for identical circuit elements in FIG.3 are omitted.

As shown in FIG. 3, a control information generation circuit 37 receivesan external signal from outside through the feed terminal 4 c, and thecontrol information generation circuit 37 feeds the control informationto the variable direct-current voltage source 32 and the offset circuit36. In the third exemplary embodiment of the present invention, theexternal signal fed from outside to the control information generationcircuit 37 includes an analog signal (i.e., a temperature signalindicating the ambient temperature). The control information generationcircuit may include an A/D conversion circuit that converts the analogexternal signal into a digital signal.

FIG. 4 is a circuit configuration of a battery pack incorporating acharge control device of a fourth exemplary embodiment of the presentinvention. The numbers appearing in FIG. 4, which are identical to thoseof FIG. 1, correspond to the same circuit elements as described inreference to the first exemplary embodiment of the present invention.Accordingly, written descriptions for identical circuit elements in FIG.4 are omitted.

As shown in FIG. 4, a control information generation circuit 37 receivesa feedback signal from the control circuit 35, and the controlinformation generation circuit 37 feeds the control information to thevariable direct-current voltage source 32 and the offset circuit 36. Inthe fourth exemplary embodiment of the present invention, the controlinformation generation circuit may include a microcomputer.

FIG. 5 is a circuit configuration of a battery pack incorporating acharge control device of a fifth exemplary embodiment of the presentinvention. The numbers appearing in FIG. 5, which are identical to thoseof FIG. 1, correspond to the same circuit elements as described above inreference to the first exemplary embodiment of the present invention.Accordingly, written descriptions for identical circuit elements in FIG.5 are omitted.

As shown in FIG. 5, a control information generation circuit 37 receivesa signal from a detection circuit 38 provided within an LSI, and thecontrol information generation circuit 37 feeds the control informationto the variable direct-current voltage source 32 and the offset circuit36. In the fifth exemplary embodiment of the present invention, aplurality of detection circuits may be provided in the LSI, and one ofthe plurality of detection circuits 38 include a temperature detectioncircuit. In addition, the control information generation circuit 37 mayinclude an A/D conversion circuit that converts the analog signal (i.e.,temperature) into a digital signal.

As discussed in the preferred embodiments of the present invention, thevariable direct-current voltage source 32 of each of the preferredembodiment can set the reference voltage (i.e., level of the chargevoltage at which the first full charge detection circuit 31 recognizesthe fully charged state) according to the control information received.In addition, the offset circuit 36 of each of the preferred embodimentscan set the offset level (i.e., level of the charge current at which thesecond full charge detection circuit 34 recognizes the fully chargedstate) likewise according to the control information received.

Moreover, adopting the charge control IC 3 of the preferred embodimentseliminate the need to connect a sense resistor externally outside thecharge control device for detecting the charge current of the secondarycell 2. This helps realize the scaling-down and cost reduction of thebattery pack 1. In addition, switch device 5 may be formed within thecharge control IC 3.

Accordingly, the charge control device of the preferred embodiments canaccurately control the charging of a secondary cell by canceling theinfluence of stress occurring when an IC is packaged or mounted on acircuit board and other factors.

It will be apparent to those skilled in art that various modificationsand variations can be made in the charge control device and battery packemploying it of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

1. A battery pack employing a charge control device, comprising: acharge detection circuit for checking whether a secondary cell is in acharged state or not based on at least a charge voltage or a chargecurrent of the secondary cell; a control circuit for controlling feedingof electric power to the secondary cell according to an output of thecharge detection circuit; and a setting circuit for setting a level ofthe charge voltage or the charge current at which the charge detectioncircuit recognizes the charged state according to control information.2. The battery pack as claimed in claim 1, further comprising: a controlinformation generation circuit receiving a control signal and generatingthe control information, wherein the setting circuit receives thecontrol information and, according to the control information, sets thelevel of the charge voltage or the charge current at which the chargedetection circuit recognizes the charged state.
 3. The battery pack asclaimed in claim 2, wherein the control signal is an analog signal. 4.The battery back as claimed in claim 2, wherein the control informationgeneration circuit generates the control information based on an outputof the control circuit.
 5. The battery pack as claimed in claim 1,further comprising: a detection circuit incorporated in the chargecontrol device and detecting a state of the charge control device,wherein, according to a result output from the detection circuit, thesetting circuit sets the level of the charge voltage or the chargecurrent at which the charge detection circuit recognizes the chargedstate.
 6. The battery pack as claimed in claim 5, further comprising: acontrol information generation circuit receiving a signal from thedetection circuit and, according to the signal from the detectioncircuit, generates the control information.